This invention relates to medical intravenous fluid-infusion apparatus, and more particularly it addresses fluid-flow type sensors thereof; for the purpose of detecting the quality and quantity of individual liquid-drop flow generally through a gravity drip-chamber assembly which may have other commercial application other than medical related.
Heretofore, there have been numerous related patent improvements in the above identified patent art field. For example, relevant early U.S. Pat. No. 2,880,764(filed May, 1957 by Pelavin for Technicon) features two vertically spaced apart devices, the upper being a photo-multiplier tube used as a triggering-device, the lower being a conventional cathode-ray video-tube utilizing a horizontal-sweep to measure droplet-width at a predetermined drop-point, the output voltage-amplitude of the camera being proportional to the diameter of the droplet; the system utilizes fixed timing-delay circuits which dictate fixed physical distances between the drop-forming orifice and the two beams, in other words requiring pre-calibrated delay-timers for each precise physical installation setup. This is a major problem when large variation in drop-size are present, due to the fact that large drops actually break away from the uppermost drop-forming orifice at a lower position, and therefore the exact drop-flight time between the upper and lower detectors is not always predictably fixed. Thus, nor is this invention readily adaptable to comparatively portable installation situations and does not tolerate significant variations in inadvertant drop-path tilt-angle, owing the change in optical image-size falling upon the camera-lens. Also, U.S. Pat. No. 3,500,366 (filed October, 1966 by Chesney for Gen.Instrument) features a single capacitive detector having dual-electrodes, which serves to detect the presence of a fluid droplet through disturbance of the electrical-field within the drip-chamber; a system which essentially serves to merely count drops, but maybe unfortunately readily upset as to reliability by proximity of ambient inductive objects or electromagnetic-fields, nor can the device read drop size.
Next, U.S. Pat. Nos. 3,563,090(filed September, 1968 by Deltour), and, 3,596,515(filed November, 1967 by Cramer for Ivac Co.) set forth fluid-flow sensor art capable of detecting and counting drops of liquid falling through a drip-chamber assembly. However, it has been found in the intervening years of usage in the field, that the so called "single blip"(electrical impulse) signal emanating from such apparatus is insufficient to provide truly adequate quality performance, in that only the number of drops is detected; yet importantly, the volume of the drops is not measured.
Later examples of liquid-drop flow-quality detector devices were found in U.S. Pat. No. 4,314,484 (filed October, 1979 by Bowman for Utah University), who demonstrate a single-blip sensor device in conjuction with ability to read variation in the quality of light-radiating from a source such as a L.E.D.(light-emitting diode); and U.S. Pat. No. 4,498,901(filed July, 1982 by Finch for Abbott Labs.) who also redemonstrates dynamic detection of droplets in the presence of changing light amplitude; and U.S. Pat. Nos. 4,397,648(filed November, 1980 by Knute for Ivac Co.), 4,509,943(filed August, 1982 by Hanzawa for T.K.Kaisha/Japan), 4,680,977(filed March, 1985 by Conero for Ivac Co.), all of which substantially mimic the notion of a single-blip liquid-drop drip-chamber flow-quanity detector means. Knute's improvement on the earlier Cramer disclosure was essentially that of an improved method of attachment to the drip-chamber, which enabled the producer(Ivac Corp.) to foster a dedicated disposable(I.V.-set) for marketing posture.
Further relevant examples of more elaborate intravenous fluid-flow delivery systems utilizing liquid-drop flow measurement apparatus, are disclosed in U.S. Pat. No. 4,718,896 (filed January, 1986 by Arndt for Abbott Labs.) who shows a plurality of radiators and oppositely cooperating photodetectors, so as to thereby better detect drops even to a 30-degree cantering of the drop-chamber. Additionally, Arndt's invention facilitated a preliminary stage photocell-detector method by which to automatically detect the presence of an alternate drop-size reducing orifice-insert(chanulas). Both the Arndt's and Conero's inventions were outgrowths of standards adopted by AAMI(Assoc.for the Advancement of Medical Instrumentation), which delt with drop-chamber angularity.
Finally, U.S. Pat. No. 4,432,761(filed September, 1982 by Dawe for Abbott Labs.) introduced the notion of a gravity-tube constriction to obtain drop-column formation, ostensibly as a predictable flow rate detector, yet the method does not readily accomodate different viscosities of fluid, and requires a specialized drip-chamber having a gravity-tube of high dimensional accuracy.
Thus, although the fluid-flow sensors discussed above have other commercial applications in their ability to detect the flow of individual droplets of a fluid, a primary use of such sensors has been the detection of fluid-flow through a drip-chamber portion of an intrevenous fluid-infusion system.